Image reading device, forming apparatus, and processing method detecting and removing perforations to correctly identify blank documents

ABSTRACT

An image reading device includes an image reading section, a first white reference member, and a control section. The image reading section reads an original document. The first white reference member is be read by the image reading section and indicates a first white reference. The control section determines whether or not a perforation image is present in the original document image indicative of the original document on a basis of an image density of a first reference image indicative of the first white reference member and an image density of the original document image.

INCORPORATION BY REFERENCE

The present application claims priority under 35 U.S.C. §119 to JapanesePatent Application No. 2013-136026, filed Jun. 28, 2013. The contents ofthis application are incorporated herein by reference in their entirety.

BACKGROUND

The present disclosure relates to image reading devices, image formingapparatuses including an image reading device, and image processingmethods.

Image forming apparatuses include an auto-document feeder toautomatically convey original documents. Automatic conveyance oforiginal documents can result in efficient reading of images of theoriginal documents and copying of the images to sheets.

Where there is a blank document among the read original documents, inorder to prevent the blank document from being copied to a sheet as itis, image forming apparatuses of some type determine whether or not ablank document is included in the original documents and performs imageprocessing to eliminate an image of an original document determined as ablank document from to-be-copied original documents.

However, where a perforation is formed in the blank original document, ashadow is casted around the perforation in image reading, therebydisabling accurate blank document determination. In view of this, imageprocessing devices of some type eliminate a predetermined region where aperforation is usually present from a determination region in advance toprevent mis-determination of a blank document.

SUMMARY

An image reading device according to the present disclosure includes animage reading section, a first white reference member, and a controlsection. The image reading section is configured to read an originaldocument. The first white reference member is configured to be read bythe image reading section and to indicate a first white reference. Thecontrol section is configured to determine whether or not a perforationimage is present in the original document image indicative of theoriginal document on a basis of an image density of a first referenceimage indicative of the first white reference member and an imagedensity of the original document image.

An image forming apparatus according to the present embodiment includesthe above image reading device and an image forming section configuredto form a toner image on a paper.

A method for processing an image according to the present disclosureincludes: reading a white reference member; reading an originaldocument; and determining whether or not a perforation image is presentin an image of the original document read in the reading an originaldocument on the basis of an image density of a reference imageindicative of the white reference member and an image density of theoriginal document image indicative of the original document.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic front cross sectional view of an image formingapparatus including an image reading device according to one embodimentof the present disclosure.

FIG. 2 is a schematic front cross sectional view of a part of the imageforming apparatus according to one embodiment of the present disclosure.

FIG. 3 is a block diagram showing a hardware configuration of the imageforming apparatus.

FIG. 4 is a flowchart depicting an image processing method that theimage reading device performs in copying or scanning.

FIGS. 5A-5C are graph representations showing distributions of imagedensity of original document images generated by reading various typesof original documents.

FIG. 6 is a flowchart depicting Step S404 in the image processing methodaccording to the present embodiment.

FIG. 7 is an illustration showing a perforation candidate region and aperforation determination region in an original document image.

FIG. 8 is a schematic front cross sectional view of the image formingapparatus including an image reading device 1A according to anotherembodiment of the present disclosure.

FIG. 9 is a flowchart depicting an image processing method that theimage reading device 1A performs in copying or scanning.

FIG. 10 is a flowchart depicting Step S604 in the image processingmethod according to one embodiment.

DETAILED DESCRIPTION

With reference to FIGS. 1-10, description will be made about embodimentsof an image reading device, an image forming apparatus, and an imageprocessing method according to the present disclosure. The presentdisclosure is not intended to be limited to any configurations describedin the following embodiments and accompanying drawings, and encompassesany configurations equivalent to the following configurations.

[Configuration of Image Forming Apparatus 100]

FIG. 1 is a schematic front cross sectional view of an image formingapparatus 100 including an image reading device 1 according to oneembodiment of the present disclosure. FIG. 2 is a schematic front crosssectional view of a part of the image forming apparatus 100 according tothe embodiment of the present disclosure. FIG. 3 is a block diagramshowing a hardware configuration of the image forming apparatus 100. Theimage forming apparatus 100 will be described below with reference toFIGS. 1-3.

The image forming apparatus 100 includes a document feeder 2, an imagereading section 3, a white reference member 27, a paper feed section 4a, a conveyance path 4 b, an image forming section 5 a, a fixing section5 b, and a control section 11.

The document feeder 2 includes an document feed tray 21 on whichoriginal documents as to-be-read objects are to be loaded, originaldocument conveyance roller pairs 22, an original document conveyancepath 23, an original document ejection roller pair 24, an originaldocument exit tray 25, a guide member 26, and an original cover 29.Original documents loaded on the document feed tray 21 are sent out tothe original document conveyance path 23 on a sheet-by-sheet basis. Thesent original documents are each guided by the guide member 26 locatedabove a sending/reading contact glass 31 provided on the top of theimage reading section 3, and are conveyed consecutively so as to come incontact with the sending/reading contact glass 31. Then, the originaldocument ejection roller pair 24 ejects the read original documents ontothe original document exit tray 25. The guide member 26 is white incolor.

The document feeder 2 is capable of being turned upward about its rearside corresponding to the rear of the paper of FIG. 1 as a pivot axis.An original document such as a book can be loaded on a loading/readingcontact glass 32 provided on the top of the image reading section 3. Theoriginal cover 29 presses an original document loaded on theloading/reading contact glass 32. The original cover 29 is white incolor. The image reading section 3 irradiates light to an originaldocument passing over the sending/reading contact glass 31 or to anoriginal document loaded on the loading/reading contact glass 32, readsan image of the original document on the basis of the reflected lightfrom the original document, and generates image data indicative of theimage of the original document. The image reading section 3 includes areading unit 61 (hereinafter also referred to as a first reading unit61).

The reading unit 61 is of contact image sensor (CIS) type and isconnected to a take-up drum 34 through a wire 33. The take-up dram 34 isrotated by a take-up motor that rotates in forward or reverse direction,thereby being capable of freely moving the reading unit 61 in thehorizontal direction, that is, the right and left directions of theimage forming apparatus 100. In order to read an original document withthe use of the document feeder 2, the reading unit 61 is secured belowthe sending/reading contact glass 31. When an original document passesover the sending/reading contact glass 31 via the original documentconveyance path 23, the light is irradiated to the original document sothat its reflected light by one line in the main scanning direction(direction orthogonal to the paper of FIG. 1) is reflected by an imagesensor (not shown) of the reading unit 61 for imaging. Then, theoriginal document is continuously conveyed so that the next line of theoriginal document in the main scanning direction is read. By contrast,in order to read an original document loaded on the loading/readingcontact glass 32, the reading unit 61 is moved in the horizontaldirection by rotation of the take-up drum 34.

Between the sending/reading contact glass 31 and the loading/readingcontact glass 32, the white reference member 27 (hereinafter alsoreferred to as a first white reference member 27) is provided toindicate a white reference. In the present embodiment, the whitereference member 27 is a plate extending in the main scanning direction(direction perpendicular to an original document conveyance direction)of the image reading device 1. The white reference member 27 has areflectivity equivalent to each reflectivity of the guide member 26 andthe original cover 29. An operating panel 10 is provided in the front ofthe image reading section 3.

The operating panel 10 is provided at the front upper part of the imageforming apparatus 100. The operating panel 10 includes a liquid crystaldisplay section 101 to display the state of the image forming apparatus100 and various types of messages. The liquid crystal display section101 displays a plurality of keys for function selection, functionsetting, character input, etc. A touch panel section 102 is provided onthe top of the liquid crystal display section 101. The touch panelsection 102 extracts a point where the user pushes in the liquid crystaldisplay section 101. Various types of hard keys including a start key103 to instruct an execution start of a function such as copying areprovided on the operating panel 10.

The paper feed section 4 a accommodates a plurality of sheets (e.g.,copy paper, plain paper, recycled paper, thick paper, OHP sheets, etc.)and sends them to the conveyance path 4 b on a sheet-by-sheet basis. Theconveyance path 4 b is a path through which a sheet is conveyed from thepaper feed section 4 a to the exit tray 41. The conveyance path 4 b isprovided with conveyance roller pairs 42 and 43 that rotate in paperconveyance, and a registration roller pair 44. The registration rollerpair 44 keeps a conveyed sheet waiting before the image forming section5 a and sends it with timing of toner image formation.

The image forming section 5 a forms a toner image on the basis of imagedata and transfers the toner image to a conveyed sheet. The imageforming section 5 a includes a photosensitive drum 51, a charger 52, anexposure device 53, a developing device 54, a transfer roller 55, and acleaner 56. The photosensitive drum 51 is supported rotatably. Thecharger 52 is arranged around the photosensitive drum 51.

The photosensitive drum 51 is provided at the central part of the imageforming section 5 a and rotates in a predetermined direction. Thecharger 52 electrostatically charges the photosensitive drum 51 to apredetermined potential. The exposure device 53 outputs laser light onthe basis of image data to scan and expose the surface of thephotosensitive drum 51, thereby forming an electrostatic latent imageaccording to the image data. The image data may be image data obtainedin the image reading section 3, image data transmitted from an externalcomputer connected through a network, or the like, for example.

The developing device 54 supplies toner to an electrostatic latent imageformed on the photosensitive drum 51 to develop the image. The transferroller 55 is in press contact with the photosensitive drum 51 to form afirst nip part. When a sheet enters the first nip part, predeterminedvoltage is applied to the transfer roller 55, thereby transferring atoner image on the photosensitive drum 51 to the sheet. The cleaner 56removes toner remaining on the photosensitive drum 51 after transfer.

The fixing section 5 b fixes a toner image transferred to a sheet. Thefixing section 5 b principally includes a heating roller 57 including aheating element, and a pressure roller 58. The heating roller 57 is inpress contact with the pressure roller 58 to form a second nip part.When a sheet passes through the second nip part, the toner on thesurface of the sheet is melt and heated, thereby fixing the toner imageto the sheet. The sheet after the toner image is fixed is received bythe exit tray 41.

The control section 11 controls each section of the image formingapparatus 100 (see FIG. 3). In one example, the control section 11includes a CPU 11 a and a storage section 11 b.

The CPU 11 a controls each section of the image forming apparatus 100 byloading and executing a control program stored in the storage section 11b. The storage section 11 b is a storage device including a ROM, a RAM,an HDD, a flash ROM, etc. The storage section 11 b stores a controlprogram, a control data, and setting data for the image formingapparatus 100, image data obtained by scanning in the image readingsection 3, etc.

The control section 11 is connected to the document feeder 2, the imagereading section 3, the paper feeder 4 a, the conveyance path 4 b, theimage forming section 5 a, the fixing section 5 b, the operating panel10, etc. The control section 11 controls operations of the respectivesections, thereby appropriately performing image formation according tothe control program and data stored in the storage section 11 b.

The control section 11 is connected to an I/F 11 c. The I/F 11 cincludes a connector, a socket, a chip for communication control, etc.The I/F 11 c connects the image forming apparatus 100 with a computer200 (e.g., personal computer or server) and a facsimile machine 300 in acommunicable manner through a network, a cable, a public line, or thelike. In one example, image data including setting data and the like canbe transmitted through the I/F 11 c to the computer 200 and thefacsimile machine 300 bi-directionally (scan function and facsimilefunction). Further, image data from the computer 200 and the facsimilemachine 300 can be accumulated in the storage section 11 b and beprinted through the I/F 11 c.

The image reading device 1 according to the present embodiment includesthe document feeder 2, the image reading section 3, and the controlsection 11. In order for the image forming apparatus 100 to perform thecopy function or the scan function, the image reading device 1 reads anoriginal document to generate original document image data indicative ofan image of the original document. In order to perform the copyfunction, the image forming section 5 a forms a toner image on a sheetaccording to original document image data, and the fixing section 5 bfixes the toner image. Thus, an image is formed on the sheet. In orderto perform the scan function, original document image data istransmitted to the computer 200 or the facsimile machine 300.

[Image Processing that Image Reading Device 1 Performs]

FIG. 4 is a flowchart depicting an image processing method that theimage reading device 1 performs. In the image processing methodaccording to the present embodiment, the image reading device 1 performsdetection of a perforation image on an image of a read originaldocument. The image processing method includes Steps S401-S405. Theimage processing method according to the present embodiment will bedescribed below with reference to FIGS. 1, 2, and 4.

Step S401: The user pushes the start key 103 in the operating panel 10to cause reading of an original document.

Step S402: In response to a request to read the original document, thereading unit 61 reads the white reference member 27 to generatereference image data. The reference image data indicates an image of thewhite reference member 27 (hereinafter referred to as a referenceimage). Data of the reference image is stored in the storage section 11b.

Step S403: After Step S402, the reading unit 61 reads the originaldocument. Specifically, the reading unit 61 reads the original documentconveyed by the document feeder 2 to generate original document imagedata indicative of an original document image.

Step S404: After the step S403, the control section 11 determineswhether or not a perforation image is present in the original documentimage on the basis of the image density of the reference image indicatedin the reference image data and the image density of the originaldocument image indicated in the original document image data.

FIGS. 5A-5C are graph representations showing distributions of the imagedensity of original document images. In FIGS. 5A-5C, the horizontal axesand the vertical axes indicate pixel position in respective originaldocuments in the sub scanning direction and image density, respectively.The lower the value of the image density on the vertical axis is, thedarker the image is. The higher the value thereof is, the brighter theimage is. Where the reading unit 61 can distinguish 256 levels of gray(8 bits), for example, a grayscale value of 0 represents black, while agrayscale value of 255 represents white. With reference to FIG. 5,description will be made below about a scheme to determine whether ornot a perforation image is present in an original document image.

FIG. 5A is a graph representation showing a distribution of the imagedensity of an original document image generated by reading an originaldocument m1. The original document m1 is perforated. In the graphrepresentation of FIG. 5A, a thick line L1 is a line passing across oneof perforations P of the original document m1 in the sub scanningdirection. A thin solid line L2 indicates a distribution of the imagedensity of the image of the original document m1 along the thick solidline L1. A broken line L3 indicates the image density of a blank regionin the original document image where no image is present. A dashed lineL4 indicates a distribution of the image density of the reference imageobtained at Step S402.

In general, a member of which color has a grayscale value closer to thewhite grayscale value than the grayscale value of the blank region ofthe original document is used as the white reference member 27. For thisreason, as shown by the broken line L3 and the dashed line L4 in FIG.5A, the image density of the reference image is higher than that of theblank region in the original document image.

When the reading unit 61 reads the original document m1, the lightreflected by the contour of each perforation P is less intense than thelight reflected by the blank region of the original document, so that ashadow lies on the contour of the perforation P. For this reason, acircular frame formed by reading the shadow of the contour appears inthe original document image. As indicated by the solid line L2 in FIG.5, in the original document, the image density of the region where thecircular frame appears is lower than that of the blank region. In otherwords, the image of the circular frame is darker than that of the blankregion.

By contrast, the light from the reading unit 61 passes through theperforation P and irradiates the guide member 26 or the original cover29 in the perforated region (region surrounded by the contour of theperforation P). Since the reading unit 61 reads the light reflected bythe guide member 26 or the original cover 29, the image density of theperforated region in the original document image is equal to that of aregion in the reference image where the perforation region of theoriginal document corresponds (region where the coordinate geometry isthe same).

FIG. 5B is a graph representation showing a distribution of the imagedensity of an original document image generated by reading an originaldocument m2. The original document m2 is an original document obtainedby copying perforated paper. Circular frames are copied in the originaldocument m2. In the graph representation of FIG. 5B, a thick solid lineL1 is a line passing across one of the circular frames of the originaldocument m2 in the sub scanning direction. FIG. 5C is a graphrepresentation showing a distribution of the image density of anoriginal document image generated by reading an original document m3.Patterns resemble to perforations are copied in the original documentm3. In the graph representation of FIG. 5C, a thick solid line L1 is aline passing across one of the patterns resembled to perforations in thesub scanning direction of the original document m3. Thin solid lines L2in FIGS. 5B and 5C indicate distributions of the image density of theimages of the original documents m2 and m3 along the thick lines L1,respectively. Respective broken lines L3 indicate the image density ofblank regions in the images of the original documents m2 and m3 where noimage is present. Respective dashed lines L4 indicate the imagedensities of the reference images obtained at Step S402.

As shown in FIGS. 5B and 5C, the original documents m2 and m3 are notperforated. For this reason, no region having an image density equal tothat of the reference image is present in the respective originaldocument images generated by reading the original documents m2 and m3.

As can be understood from the explanation with reference to FIGS. 5A-5C,a region having an image density equal to that of the reference image ispresent in the original document image of a perforated originaldocument. By contrast, no region having an image density equal to thatof the reference image is present in the original document image of anon-perforated original document. In view of this, at Step S404, thecontrol section 11 compares the pixels in the original document imagewith the corresponding pixels in the reference image to detect, in theoriginal document image, any pixel having an image density equal to thatof the reference image. The control section 11 determines whether or nota perforation image is present in the original document image accordingto a result of detection of the pixel having the equal image density.

FIG. 6 is a flowchart depicting Step S404 in the image processing methodaccording to the present embodiment. Step S404 is performed throughSteps S501-S505. FIG. 7 is an illustration showing a perforationcandidate region and a perforation determination region in an originaldocument image. Step S404 will be described below with reference toFIGS. 6 and 7.

Step S501: The control section 11 analyses an original document image todetect a circular frame from the original document image. As shown inFIG. 7, circular frames of perforations appear in the left end part ofan original document image in many cases. The control section 11 detectseach circular frame in the left end part of the original document imageshown in FIG. 7. The circular frame can be detected by pattern matching,for example. When no circular frame is detected, the routine for theimage processing proceeds to Step S505. By contrast, when a circularframe is detected, the control section 11 extracts a region includingthe circular frame as a perforation candidate region A1. Then, theroutine proceeds to Step S502.

Step S502: The control section 11 sets, as a perforation determinationregion A2, a circular region with a radius that is a half of thedistance from a center C to the circumference of the circular frame inthe perforation candidate region A1 extracted at Step S501. Then, theroutine proceeds to Step S503.

Step S503: The control section 11 determines whether or not the rate ofpixels having an image density equal to that of the pixels in thereference image based on all the pixels in the perforation determinationregion A2 exceeds a predetermined threshold value. The threshold valueis stored in the storage section 11 b. The threshold value is 60% of thepixels in the perforation determination region A2, for example. When therate of the pixels having the equal density does not exceed thethreshold value, the routine proceeds to Step S505. By contrast, whenthe rate of the pixels having the equal density exceeds the thresholdvalue, the routine proceeds to Step S504.

Step S504: When the rate of the pixels having an image density equal tothat of the reference image based on all the pixels in the perforationdetermination region A2 exceeds the threshold value, the control section11 determines that a perforation image is present in the perforationcandidate region A1. Then, the image processing is ended.

Step S505: On the basis of the result that no circular frame is detected(NO at Step S501), or that the rate of the pixels having the equal imagedensity does not exceed the threshold value (NO at Step S503), thecontrol section 11 determines that no perforation image is present inthe original image. Then, the image processing is ended.

With reference to FIGS. 1-7, description has been made about the imageforming apparatus 100 including the image reading device 1 and the imageprocessing method that the image reading device 1 performs according tothe present embodiment. According to the image reading device 1 of thepresent embodiment, a perforation image in an original document imagegenerated by reading an original document can be detected without needof any complicated detection mechanisms and any intricate detectionsteps.

Additional image processing such as determination of a blank documentand/or deletion of a perforation image may be performed upon detectionof a perforation image in the image reading device 1 of the presentembodiment. Determination of a blank document is performed in a mannerthat upon determination that a perforation image is present in anoriginal document image, the control section 11 eliminates theperforation candidate region A1 including the perforation image from aregion to be subjected to blank document determination, and thendetermines whether or not the original document is a blank document.Upon determination that the original document is a blank document, thecontrol section 11 deletes the original document image, for example. Aperforation image is deleted in a manner that upon determination that aperforation image is present in an original document image, the controlsection 11 deletes the perforation image (e.g., circular frame).

It is noted that the control section 11 detects a circular frame fromthe left end part of an original document image in the abovedescription, which however, should not be taken to limit the presentdisclosure. Detection of a circular frame in an entire original documentimage enables the control section 11 to detect a circular frame copiedin a region other than the left end part (e.g., central part) of theoriginal document image for determination of the presence of aperforation image.

The image reading device 1 in the embodiment described with reference toFIGS. 1-7 detects a perforation image in an original document imagegenerated by reading one of the sides of the original document, whichhowever, should not be taken to limit the present disclosure, asdescribed with reference to FIG. 8.

FIG. 8 is a schematic front cross sectional view of an image formingapparatus 100 including an image reading device 1A according to anotherembodiment of the present disclosure. The image reading device 1A hasthe same configuration as that described with reference to FIG. 1 exceptfurther inclusion of a reading unit 62 (hereinafter also referred to asa second unit 62). Therefore, duplicate description thereof is omitted.

The second reading unit 62 is provided on the original documentconveyance path 23. The second reading unit 62 is of CIS type. Thesecond reading unit 62 is provided between the sending/reading contactglass 31 and the original document ejection roller pair 24, for example.The second reading unit 62 reads the reverse side of an originaldocument subjected to duplex printing. Accordingly, one-time passing ofsuch an original document through the original document conveyance path23 can result in reading of both the opposite sides of the originaldocument. Thus, both the opposite sides of the original document can beeasily read without need of turning over the conveyance direction of anoriginal document and provision of complicate original documentconveyance path.

A white reference member 28 (hereinafter also referred to as a secondwhite reference member) to indicate a white reference is provided toface the second reading unit 62. The second white reference member 28 isa guide plate extending in the main scanning direction of the imagereading device 1A. The second white reference member 28 has an imagedensity different from that of the first white reference member 27. Itis noted that a roller may be provided as the second white referencemember 28 rather than the guide plate.

[Image Processing that Image Reading Device 1A Performs]

FIG. 9 is a flowchart depicting an image processing method that theimage reading device 1A performs. In the image processing methodaccording to the present embodiment, the image reading device 1Aperforms perforation image detection on a first original document imagegenerated by reading one side (hereinafter referred to as a first side)of an original document and on a second original document imagegenerated by reading the opposite side (hereinafter referred to as asecond side) thereof. The image processing method includes stepsS601-S604. The image processing method according to the presentembodiment will be described below with reference to FIGS. 8 and 9.

Step S601: The user pushes the start key 103 in the operating panel 10to cause reading of an original document.

Step S602: In response to a request to read the original document, thefirst reading unit 61 (see FIG. 2) reads the first white referencemember 27 to generate first reference image data. The first referenceimage data indicates an image of the first white reference member 27(hereinafter referred to as a first reference image). On the other hand,the second reading unit 62 reads the second white reference member 28 togenerate a second reference image data. The second reference image dataindicates an image of the second white reference member 28 (hereinafterreferred to as a second reference image). The first and second referenceimage data is stored in the storage section 11 b.

Step S603: After Step S602, the reading units 61 and 62 read theoriginal document. Specifically, the first reading unit 61 reads thefirst side of the original document conveyed by the document feeder 2 togenerate first original document image data. The first original documentdata indicates an image of the first side of the original document(hereinafter referred to as a first original document image). The secondreading unit 62 reads the second side of the original document conveyedby the document feeder 2 to generate second original document imagedata. The second original document data indicates an image of the secondside of the original document (hereinafter referred to as a secondoriginal document image).

Step S604: After Step S603, the control section 11 determines whether ornot a perforation image is present in the first original document imageon the basis of the image density of the first reference image indicatedin the first reference image data and the image density of the firstoriginal document image indicated in the first original document imagedata. The control section 11 also determines whether or not aperforation image is present in the second original document image onthe basis of the image density of the second reference image indicatedin the second reference image data and the image density of the secondoriginal document image indicated in the second original document imagedata.

FIG. 10 is a flowchart depicting Step S604 in the image processingmethod according to the present embodiment. Step S604 is performedthrough Steps S701-S711.

Step S701: The control section 11 analyses the first original documentimage to detect a circular frame in the first original document image.When no circular frame is detected, the routine for the image processingproceeds to Step S711. By contrast, when a circular frame is detected,the control section 11 extracts a region including the circular frame asa perforation candidate region A1 (see FIG. 7). Then, the routineproceeds to Step S702.

Step S702: The control section 11 sets, as a perforation determinationregion A2 (see FIG. 7), a circular region with a radius that is a halfof the distance from the center C to the circumference of the circularframe in the perforation candidate regions A1 extracted at Step S701.Then, the routine proceeds to Step S703.

Step S703: The control section 11 determines whether or not the rate ofpixels having an image density equal to that of the pixels in the firstreference image based on all the pixels in the perforation determinationregion A2 exceeds a predetermined threshold value. When the rate of thepixels having an image density equal to that of the first referenceimage does not exceed the threshold value, the routine proceeds to StepS711. By contrast, when the rate of the pixels having an image densityequal to that of the pixels in the first reference image exceeds thethreshold value, the routine proceeds to Step S704.

Step S704: When the rate of the pixels having an image density equal tothat of the pixels in the first reference image based on all the pixelsin the perforation determination region A2 exceeds the threshold value,the control section 11 determines that a first side perforationcandidate image is present in the perforation candidate region A1 of thefirst original document image. Then, the routine proceeds to Step S705.

Step S705: The control section 11 analyses the second original documentimage to detect a circular frame in the second original document image.When no circular frame is detected, the routine for the image processingproceeds to Step S711. By contrast, when a circular frame is detected,the control section 11 extracts a region including the circular frame asa perforation candidate region A1. Then, the routine proceeds to StepS706.

Step S706: The control section 11 sets, as a perforation determinationregion A2, a circular region with a radius that is a half of thedistance from the center C to the circumference of the circular frame inthe perforation candidate region A1 extracted at Step S705. Then, theroutine proceeds to Step S707.

Step S707: The control section 11 determines whether or not the rate ofpixels having an image density equal to that of the pixels in the secondreference image based on all the pixels in the perforation determinationregion A2 exceeds a predetermined threshold value. When the rate of thepixels having an image density equal to that of the pixels in the secondreference image does not exceed the threshold value, the routineproceeds to Step S711. By contrast, when the rate of the pixels havingan image density equal to that of the pixels in the second referenceimage exceeds the threshold value, the routine proceeds to Step S708.

Step S708: When the rate of the pixels having an image density equal tothat of the pixels in the second reference image based on all the pixelsin the perforation determination region A2 exceeds the threshold value,the control section 11 determines that a second side perforationcandidate image is present in the perforation candidate region A1 in thesecond original document image. Then, the routine proceeds to Step S709.

Step S709: The control section 11 determines whether or not the firstand second perforation candidate images are present in regionscorresponding to each other in the first and second original documentimages, respectively. In one example, the control section 11 calculatesthe coordinate geometry of the first side perforation candidate image inthe first original document image and determines whether or not thesecond side perforation candidate image is present in the samecoordinate geometry of the second original document region image.Alternatively, the control section 11 may calculate the coordinategeometry of the second side perforation candidate image in the secondoriginal document image and determines whether or not the first sideperforation candidate image is present in the same coordinate geometryof the first original document region image. When it is determined thatthe first and second perforation candidate images are present in therespective regions corresponding to each other, the routine proceeds toStep S710. By contrast, when it is determined that neither the first norsecond perforation candidate images is present in the respective regionscorresponding to each other, the routine proceeds to Step S711.

Step S710: When it is determined that the first and second perforationcandidate images are present in the respective regions corresponding toeach other at Step S709, the control section 11 determines that aperforation image is present in each of the first and second originaldocument images. Then, the image processing is ended.

Step S711: Upon detection of no circular frame in the first originaldocument image (NO at Step S701), or detection of no circular image inthe second original document image (NO at Step S705), the controlsection 11 determines that no perforation image is present in the firstand second original document images. Then, the image processing isended. The control section 11 also determines that no perforation imageis present in the first and second original document images on the basisof the result that the rate of the pixels having the equal image densitydoes not exceed the threshold value (NO at Step S703 or S707). Then, theimage processing is ended. Or, the control section determines that noperforation image is present in the first and second original documentson the basis of the result of determination that neither the firstperforation candidate image nor the second perforation candidate imageis present in the regions corresponding to each other in the oppositesides of the original document (NO at S709). Then, the image processingis ended.

Description has been made about the image forming apparatus 100including the image reading device 1A and the image processing methodthat the image reading device 1A performs according to one embodimentwith reference to FIGS. 8-10. Where determination as to whether or not aperforation image is present is performed on an original document imagegenerated by reading one side of an original document of which blankregion has an image density rather close to the image density of thewhite reference member, a perforation image may not be discriminatedagainst the image of the blank region in the original document image. Inview of this, the image density of the first reference member 27 isdifferentiated from that of the second reference member 28 in the imagereading device 1A according to the present embodiment. In general, blankregions on the respective opposite sides of an original document have anequal image density. Therefore, even when the image density of the blankregion on one of the sides is equal to that of one of the whitereference members (e.g., the first white reference member 27), the imagedensity of the blank region on the other side is different from that ofthe other white reference member (e.g., the second white referencemember 28). Accordingly, when the first and second perforation imagesare present in the respectively corresponding regions of the first andsecond original document images generated by reading the respectivesides of an original document, the presence of the perforation image isdetermined in the image reading device 1A of the present embodiment.Thus, a perforation image can be detected accurately. Upon detection ofa perforation image, the image reading device 1A may also performadditional image processing such as determination of a blank documentand/or deletion of a perforation image.

The image density of the first white reference member 27 is differentfrom that of the second white reference member 28 in the embodimentdescribed with reference to FIGS. 8-10, which however, should not betaken to limit the present disclosure. The image density of the firstwhite reference member 27 may be equal to that of the second whitereference member 28. In this case, a perforation image can be detectedin the first and second original document images generated by readingthe respective sides of an original document including blank regions onthe respective sides having an image density different from that of thefirst and second white reference members 27 and 28.

The first reading unit 61 is of CIS type in each of the aboveembodiments. However, the present disclosure is not limited to this. Thefirst reading unit 61 may be of CCD type including an optical systemwith a lamp and a mirror.

Further, the reference image data is obtained by reading the whitereference member each time a request to read an original document isreceived, which however, should not be taken to limit the presentdisclosure. The reference image data indicative of the white referencemember may be stored in the storage section 11 b in advance so that aperforation image is detected by comparing original document image datagenerated by reading an original document with the reference image datastored in the storage section 11 b.

In addition, the reference image data is obtained by reading the whitereference member 27 in the above embodiment. Alternatively, the guidemember 26 or the original cover 29 may be used as a white referencemember in a manner to obtain the reference image data by reading theguide member 26 or the original cover 29 before an original document isread. In a region where a perforation P is formed, the light from thereading unit 61 passes through the perforation P to irradiate the guidemember 26 or the original cover 29, so that the reading unit 61 readsthe reflected light from the guide member 26 or the original cover 29.Accordingly, when the reference image data is obtained by reading theguide member 26 or the original cover 29, appropriate detection of aperforation can be performed.

It is noted that the control section 11 sets, as the perforationdetermination region A2, a circular region with a radius that is a halfof the distance from the center C to the circumference of the circularframe in the perforation candidate region A1 in the above embodiment.However, the control section 11 may set, as the perforationdetermination region A2, a circular region with a radius that is 1/n ofthe distance from the center C to the circumference of the circularflame, where n is larger than 1. In one example, the distance from thecenter C to the circumference of a circular frame may be ⅓.

What is claimed is:
 1. An image reading device comprising: an imagereading section configured to read an original document; a first whitereference member configured to be read by the image reading section andto indicate a first white reference; a control section configured todetermine whether or not a perforation image is present in the originaldocument image indicative of the original document on a basis of animage density of a first reference image indicative of the first whitereference member and an image density of the original document image;and a second white reference member configured to be read by the imagereading section and to indicate a second white reference, wherein theoriginal document has a first side and a second side opposite to thefirst side, the image reading section includes: a first reading unitconfigured to read the first white reference member and the first sideof the original document; and a second reading unit configured to readthe second white reference member and the second side of the originaldocument, the control section determines whether or not a first sideperforation candidate image is present in a first original documentimage indicative of the first side of the original document on a basisof the image density of the first reference image and an image densityof the first original document image, while determining whether or not asecond perforation candidate image is present in a second originaldocument image indicative of the second side of the original document ona basis of the image density of a second reference image indicative ofthe second side of the original document and an image density of thesecond original document image, and the control section determineswhether or not the perforation image is present in the first and secondoriginal document images on a basis of a result of determination as towhether or not the first and second side perforation candidates arepresent in the respective regions corresponding to each other in thefirst and second original document images.
 2. The image reading deviceaccording to claim 1, wherein the image density of the first whitereference member is different from that of the second white referencemember.
 3. The image reading device according to claim 1, wherein thecontrol section eliminates a region including the perforation image anddetermines whether or not the original document is a blank document on abasis of a result of determination.
 4. The image reading deviceaccording to claim 1, wherein the control section deletes theperforation image on a basis of a result of determination.
 5. An imageforming apparatus, comprising: the image reading device according toclaim 1; and an image forming section configured to form a toner imageon a sheet.
 6. An image reading device comprising: an image readingsection configured to read an original document; a first white referencemember configured to be read by the image reading section and toindicate a first white reference; and a control section configured todetermine whether or not a perforation image is present in the originaldocument image indicative of the original document on a basis of animage density of a first reference image indicative of the first whitereference member and an image density of the original document image,wherein the control section extracts a perforation candidate regionincluding a circular frame from the original document image, the controlsection determines whether or not the perforation image is present inthe original document image on a basis of the image density of the firstreference image and an image density of the perforation candidate regionof the original document image, the control section sets a circularregion with a radius that is 1/n of a distance from a center to acircumference of the circular frame in the perforation candidate regionas a perforation determination region, wherein n is larger than 1, andthe control section determines whether or not the perforation image ispresent in the original document image on a basis of the image densityof the first reference image and an image density of the perforationdetermination region in the original document image.
 7. The imagereading device according to claim 6, wherein n is
 2. 8. The imagereading device according to claim 6, further comprising: a storagesection configured to store a threshold value set in advance, whereinthe control section determines whether or not the perforation image ispresent in the original document image in a manner to determine whetheror not a rate of pixels having an image density equal to the imagedensity of the first reference image based on all pixels of theperforation determination region exceeds the threshold value.
 9. Theimage reading device according to claim 6, wherein the control sectioneliminates a region including the perforation image and determineswhether or not the original document is a blank document on a basis of aresult of determination.
 10. The image reading device according to claim6, wherein the control section deletes the perforation image on a basisof a result of determination.
 11. An image forming apparatus,comprising: the image reading device according to claim 6; and an imageforming section configured to form a toner image on a sheet.